The present invention relates to an improved molten metal sample cup for detecting phase changes, thermal arrest temperatures, and the like of molten metal such as cast iron, steel and the like. Cups of this general type are known. For example, see U.S. Pat. No. Re. 26,409; U.S. Pat. No. 3,546,921; and U.S. Pat. No. 4,059,996.
U.S. Pat. No. 3,546,921 discloses a method of producing an initial thermal arrest in the cooling curve of a molten sample of hypereutecic cast iron by introducing into the sample a stabilizing additive which retards primary graphite formation as the molten sample cools. The stabilizer is added in the form of a pellet or in particulate form. The stabilizing additive is not controlled in any manner with respect to regulating the rate at which the additive is dispersed into the molten metal. As a result, the additive tends to become burned up and not available for white solidification. Further, there is a tendency for the additive to rise to the surface of the molten metal as a slag.
U.S. Pat. No. 4,059,996 sets forth an improvement over the other two patents by disclosing a blob of material in contact with the bottom wall of a cavity. The blob of material includes a carbide formation promoting material mixed with a refractory material and preferably mixed with a material for evolving hydrogen. The refractory material aids in preventing the carbide formation promoting material from being burned up quickly and mixing too quickly with the molten metal. As the size and shape of the blobs differ, so does the surface areas of the blobs differ. The rate at which the additive which promotes the formation of carbides is released into the molten metal is an ever-changing rate that is controlled by the blob surface area which also changes.
In connection with such sample cups, the initial activity of boiling is an uncontrolled happening that influences the final results. It has been found that where boiling is of a minor nature, there is a metal loss of a percent or two. Cups that have greater activity or more pronounced boiling, can result in a metal loss of as much as ten percent. A change in the amount of metal in the sample produced different results when the blobs are of uniform amount.
The present invention is directed to a solution of the problems associated with the prior art and in particular regulation of the dispersion of the additive into the molten iron in a manner which is simple and inexpensive while obtaining more uniformity in results.